Thermoelectric device



Patented July 1, 1952 games 1 York No Drawing. Application June 3,

Serial No. 166,073

6 Claims. 1

The present invention relates to a thermoelectric device. Moreparticularly, it is concerned with an improved thermoelectric elementand to thermocouples comprising such element.

An object of the present invention is to provide a thermoelectric alloyhaving a high thermal electric power which is not materially affected bythe presence of impurities.

A further object of the invention is to provide a thermoelectric alloyhaving good mechanical strength, said alloy being malleable attemperatures below red heat.

These principal objects of the invention and others which will becomeapparent from the following description are attained in accordance withthe present invention by providing a new and improved thermoelectricalloy composed of silver and tellurium and containing more than 63%silver. The alloys found to be useful for obtaining the above mentionedobjects are those containing from 63 to 80% silver, preferably from 63to 65% silver, balance tellurium except for minor impurities.

Investigation of the thermoelectric properties of silver-telluriumalloys has shown that at a point at or near the compositioncorresponding to 62.8% silver, the polarity of the thermal E. M. F. ofthe alloy reverses. For example, an alloy with 60% silver has a thermalE. M. F. of plus 150 microvolts per degree 0. against copper, while analloy with 65% silver has a thermal E. of minus 100 microvolts perdegree C. against copper. These alloys of silver and telluriumcontaining more than 63% silver are also characterized by goodmechanical strength, good malleability and an E. M. F. which is notmaterially affected by the presence of impurities. For ex ample, the 65%silver alloy of tellurium appears to be unique among alloys having sucha high thermal E. M. F. in that it is also malleable at temperaturesbelow red heat. At a temperature of about 400 C. this alloy may behammered from a rod .1" in diameter to a strip about .04" or less inthickness. This property is particularly useful in the manufacture ofsmaller thermocouple elements as, for example, for instrumentthermocouple applications. The 65% silver alloy has a resistivity ofabout .0048 ohm per centimeter cube.

The thermoelectric alloys of the present inven-.

tion can be made by adding the required amount of silver to moltentellurium in a porcelain crucible. The silver rapidly dissolves when thetellurium is at a temperature barely above its melting point. Thereafterthe molten alloy is cast into a suitable form and the cast productformed at an elevated temperature into the required final shape.

While the thermoelectric alloys of the present invention can be usedwith any suitable second alloy or element in the manufacture ofthermocouples, highly eificient thermocouples are those in which thesilver-tellurium thermoelectric alloy of the present invention comprisesone of the elements while the second element is one having a highpositive thermal E. M. F. For this purpose the second element preferablycomprises impure tellurium or alloys of silver and tellurium containingless than 62% silver. M. F. of impure tellurium is the highestobtainable in materials which have a resistivity low enough to give areasonably good efficiency. Since its thermal E. M. F. is positive withrespect to copper, ranging from 200' to 550 microvolts per degree C.,the combination of impure tellurium and the high silver tellurium alloysprovides a thermocouple of maximum efficiency.

The preferred impurities in the tellurium element are up to 1% antimonyor bismuth. An alloy of .5% antimony,balance tellurium has a thermal E.M. F. of 215 microvolts per degree C. while an alloy of 1% bismuth,balance tellurium has a thermal E. M. F. of a positive 220 microvoltsper degree C. Both form excellent thermocouple combination with thesilver-tellurium alloys.

As was indicated hereinbefore, alloys of tellurium and silver containingless than 62.8% silver,

as, for example, an alloy containing silver, has a thermal E. M. F. ofplus 150 microvolts per degree C. and these can also be employed withthe present thermocouple elements. For better workability alloyscontaining from 50 to about 62% silver are preferred as they moreclosely resemble the higher silver alloys'in workability than do thealloys containing less silver.

By the term impurities as used hereinbefore in connection with the alloyof silver and tellurium containing at least 63% silver, it is intendedto cover those impurities inherent in commercial tellurium and silverand hence present in the final alloys.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A thermocouple comprising a negative thermoelectric element composedof an alloy consisting of tellurium and silver and containing from 63%to silver.

2. A thermocouple comprising one element The thermal E.

3 composed of an alloy of tellurium and silver containing from 63% to65% silver.

3. A thermocouple of claim 1 in which the second element is composed ofimpure tellurium.

4. A thermocouple element of claim 3 in which the impurities are bismuthor antimony.

5. A thermocouple of claim 1' in which the second element is composed ofa tellurium-silver alloy containing less than 62% silver.

6. A thermocouple comprising elements composed of alloys of silver andtellurium, one of said elements consisting of an alloy containing 63% to65% silver, balance tellurium, and the other element consisting of lessthan 62% silver, balance tellurium.

HAROLD T. FAUS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,232,960 Milnes Feb. 25, 19412,264,073 Faus Nov. 25, 1941 2,397,756 Schwartz Apr. 2, 1946 OTHERREFERENCES Addicks: "Silver in Industry," 1940, pages 111, 112, 532,published by Reinhold Pub. Corp.', New York city.

Homing et a1, Review of Scientific Instruments (July 1947), vol. 18, No.7, pp. 477-478.

1. A THERMOCOUPLE COMPRISING A NEGATIVE THERMOELECTRIC ELEMENT COMPOSEDOF AN ALLOY CONSISTING OF TELLURIUM AND SILVER AND CONTAINING FROM 63%TO 80% SILVER.